Systems are known for providing synchronizing signals to pluralities of visible or audible/visible alarm indicating output devices. One such system has been disclosed in Karim et al U.S. Pat. No. 5,598,139 assigned to the assignee hereof and incorporated by reference.
Control of the audible devices or the audible portion of audible/visual devices enables output of a variety of alarm indicating audible outputs. Since it is known to be desirable to couple the number of audible, visible or audible/visible devices to a common loop and synchronize the visible devices on the loop, it would be desirable to incorporate audible control sequences into the synchronization process. Preferably, such an enhancement could be implemented so as to impose minimal technical and financial costs on the output devices. It would also be preferable if the control information conveying process was compatible with conventional ways in which such output devices are operated.
As is known, such output devices are usually driven by a reverse polarity signal, when inactive, for purposes of supervising the communication lines. To activate the output devices, the polarity is reversed providing electrical energy to the devices, at a predetermined voltage. This power carrying signal is interruptible for purposes of synchronizing visual output devices coupled to the link, as taught by Karim et al U.S. Pat. No. 5,598,139. Such synchronizing signals usually take the form of pulses from the predetermined voltage going to a ground level for the loop and then returning to the predetermined voltage.